UN staff members are said to be among those killed.
An Israeli military spokesman said the strikes signalled a “gradual increase in the pressure” on Hamas.
Power plant destroyed
Gazans get power from just one local plant, as well as some supplies from Israel and Egypt.
On Tuesday morning a huge plume of smoke rose over the strip’s only power plant after one of its fuel tanks was reportedly set alight by Israeli tank shells, and the facility was forced to shut down.
A fuel depot supplying Gaza’s only power station has been hit, as Martin Patience and Chris Morris report
For the last three weeks, most Gazans have been living with just a few hours of electrical supplies – now the situation will almost certainly get worse.
After a brief lull in the fighting earlier this week, the violence has returned with a renewed intensity.
In Gaza City you can hear the constant bombardment of areas close to the Israeli border. There have also been large explosions in the city throughout the morning.
Any sign that a patchwork of truces would lead to more a sustainable ceasefire has been dashed for now.
The Israeli military is stepping up its offensive to find and destroy Hamas tunnels, as Bethany Bell reports
More than three weeks on there is in general very widespread support among Israelis for the Gaza offensive. Recent polls say almost 90% of Israelis are in favour.
Some are beginning to ask whether the army and the government underestimated the tunnel threat from Gaza. Targeting the tunnels is one of Israel’s main objectives in this campaign, but destroying them is complicated.
Israel says it has identified more than 30 tunnels – but the army was taken off guard last night when five soldiers were killed by Palestinian militants who came up through a tunnel into Israel.
Military sources say these aren’t just single shafts but a labyrinth of underground passageways, some booby-trapped with explosives.
The government says it will not stop the offensive until the tunnels are destroyed.
In a televised address on Monday, Prime Minister Benjamin Netanyahu stressed the need to destroy tunnels dug under the Gaza-Israel border, to prevent militants infiltrating Israel.
After Tuesday’s loss of life in Gaza a Palestinian official in the West Bank said rival Palestinian factions had agreed to a unilateral truce lasting 24 hours.
Yasser Abed Rabbo of the Palestine Liberation Organization said he spoke for Hamas, but a spokesman for the group, Sami Abu Zuhri, quickly denied that.
“Hamas gave no approval to anything Abed Rabbo said,” Reuters reported him saying.
Palestinian officials now say 1,156 Palestinians, most of them civilians, have been killed in the fighting since 8 July. Some 6,700 have been injured.
Israel has lost 53 soldiers and three civilians – two Israelis and a Thai worker.
Fifty-five houses were destroyed in overnight bombing, with people buried under rubble in at least three of them, Palestinian security sources told the BBC.
The unoccupied house of former Hamas Prime Minister Ismail Haniyeh was destroyed.
The Israeli air strikes destroyed the house of ex-Hamas Prime Minister Ismail Haniyeh, as Chris Morris reports
A neighbour, Um Hani Abu Ryalah, told AP news agency the experience had terrified her family: “Our children… can’t hear because of the loud explosions and they are shaking.”
Israeli fire is also said to have damaged the Hamas TV and radio stations, three mosques, four factories and government buildings.
Gaza’s port was also destroyed, Palestinian security sources told the BBC, and two schools and a kindergarten were on fire after being hit.
Among the 100 people killed on Tuesday were seven families, the Palestinian health ministry said.
UN Relief and Works Agency spokesman Chris Gunness said in a tweetthat a number of staff members had reportedly been killed. The UN is currently caring for 182,604 Palestinians in its 82 shelters in Gaza, he said.
Rockets fired from Gaza continued to hit Israel on Tuesday.
Lt-Col Peter Lerner, an Israeli military spokesman, told AP pressure was being increased on Hamas.
“Israel is determined to strike this organisation and relieve us of this threat,” he said.
On Monday, five Israeli soldiers were killed when militants infiltrated the border, while a mortar bomb killed four earlier and a tenth died in a clash in southern Gaza, the Israeli army said.
In his address on Monday night, Mr Netanyahu said Gaza had to be demilitarised in order to protect Israel.
“We will not finish the operation without neutralising the tunnels, which have the sole purpose of destroying our citizens, killing our children,” he said.
Israel’s Operation Protective Edge began on 8 July after a surge in militant rocket attacks.
A rally in support of the operation is planned for Tuesday evening in Tel Aviv.